First-principles based design of new visible-light absorbing ferroelectrics

Due to an inexhaustible supply of energy from the sun and the lack of emissions, conversion of sunlight into electricity by photovoltaics (PVs) is the most promising long-term sustainable energy technology. Recent experimental and theoretical worked has shown that ferroelectric (FE) oxides may be a new promising candidate class of materials for PV applications due to the bulk photovoltaic effect which in principle can enable beyond the Shockley-Queiser (SQ) limit power conversion efficiency (PCE). In this work, using first-principles calculations, we investigate the band-engineering of ferroelectric perovskite oxides to obtained candidate material for FE PV. We use substitution of Mo⁶⁺ and W⁶⁺ cations into the classic BaTiO₃ ferroelectric to obtain materials with a high polarization but lower band gaps than that of the parent BaTiO₃ material. We expect that lower band gaps will be obtained in Mo⁶⁺ and W⁶⁺-doped BaTiO3 due to the higher electronegativity of the Mo⁶⁺ and W⁶⁺ compared to the Ti⁴⁺ of BaTiO3. Using the results of first-principles calculations, we study how structural changes in BaTiO₃ due to strain, change of phase and the substituent content affect the band gap and the polarization of the material. It is found that several compositions exhibit the desired combination of polarization and band gap and are likely to be promising for use in FE PV devices.